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The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near‐field of the sample (

A hybrid near‐field/fiber laser probe has been developed for high flux, reflection mode optical imaging of surfaces on a subwavelength scale. Spatial resolution of ∼100 nm (i.e., ∼λ/10 at λ=1060 nm) has been achieved simultaneously with signals of ∼1014–1015 photons/s, an improvement of ∼103–104 over earlier designs. The probe thus represents an important step in the development of advanced near‐field transducers for high bandwidth applications such as high density data storage.

Modulation‐doped GaAs/AlGaAs quantum wires have been fabricated using electron‐beam lithography followed by electron‐cyclotron resonance reactive ion etching to selectively deplete the electron gas. This technique has the advantages of low damage to the quantum well, strongly anisotropic etching, and reproducible control over the etch depth. The quantum wires exhibit high photoluminescence efficiencies when etched as close as 200 A to the electron gas. The fundamental gaps show the large optical red shifts associated with strongly spatially indirect transitions. The spacings between one‐dimensional subbands determined from inelastic light scattering measurements are larger than 2 meV.

We demonstrate the use of an ultrathin (≊5 nm) Si layer deposited on InP substrates as a mask in selective area epitaxy of InGaAs by metalorganic molecular beam epitaxy. Patterns of varying shapes and sizes, from 5 to 0.5 μm, were written on the mask by focused Ga ion beam and etched by Cl2. The growth rate of InGaAs was studied by scanning force microscopy using stripes with guard rings spaced as close as 0.5 μm from the stripes. A small increase in the growth rate was detected only when the feature size was lower than 5 μm, and the growth rate was not affected by the presence of the guard rings. This shows that precursor material is being transferred from the slow growing {111}‐planes to the (100)‐plane, and that migration of species from the Si mask to the growing areas is negligible.

A distance regulation method has been developed to enhance the reliability, versatility, and ease of use of near‐field scanning optical microscopy (NSOM). The method relies on the detection of shear forces between the end of a near‐field probe and the sample of interest. The system can be used solely for distance regulation in NSOM, for simultaneous shear force and near‐field imaging, or for shear force microscopy alone. In the latter case, uncoated optical fiber probes are found to yield images with consistently high resolution.

We report the fabrication of strong Bragg reflectors embedded into fiber matched silica on silicon waveguides. First order gratings are dry etched into the waveguide core and are covered with a thin Si3N4 layer prior to cladding deposition. Reflection bands 225 A wide for TE and 193 A wide for TM polarizations are obtained with 200 A Si3N4 cover layers. The TE and TM spectra are overlapping, resulting in nearly polarization independent Bragg reflectors.

Heterostructures of InGaAs/InP have been grown selectively through windows in SiO2‐masked InP substrates using metalorganic molecular beam epitaxy. The structures show high cathodoluminescence efficiency for window sizes down to 5 μm. A significant red shift, consistent with compressive lattice strain, and reduced intensity are observed for smaller features. Anomalous growth is observed near the edges of the windows. Selectively grown InGaAs/InP p‐n junctions and bipolar transistors exhibit excellent electrical characteristics after removal of 1–2 μm of edge material.

We demonstrate the novel application of the scanning tunneling microscope to find and probe the electronic transport properties of single semiconductor nanostructures at temperatures from room temperature to as low as 1.5 K. The current‐voltage characteristics of InGaAs/InAlAs resonant tunneling nanostructures clearly show negative differential resistance. From the dependence of the current on cross‐sectional area the lateral depletion is estimated to be 300 A.

We have developed a complete lithographic process combining focused ion beam writing, dry etching, and molecular beam epitaxy for in situ preparation of buried InP‐based microstructures. A focused ion beam is used to locally remove an ultrathin oxide imaging layer grown in situ on the surface of InP. The pattern is transferred into the underlying semiconductor by free Cl2 etching with the patterned oxide layer acting as an etch mask. After removal of the oxide mask, GaInAs/InP heterostructures with excellent morphology and high luminescence efficiency can be grown on the patterned substrate. The entire process of mask formation, lithography, and regrowth can be carried out in situ repeatedly, and used for creating fully buried microstructures.

The biaxial tensile stress of 2.65 kbar in as‐grown GaAs/Si is reduced by post‐growth patterning of the GaAs and the reduction in stress is dependent on the pattern size and shape. For stripe patterns less than 15 μm wide the stress becomes largely uniaxial with stress relief normal to the stripe direction. Rectangular patterns exhibited stress relief in orthogonal directions, and have the lowest stress in the narrow direction of the rectangle. A 9×12 μm2 rectangle exhibited an average stress of 0.5 kbar.

We have performed a semi‐empirical calculation of the refractive index changes induced by a perpendicular electric field in quantum wells. This calculation is based on experimental electroabsorption data, together with absorption sum rules that have recently been developed. We find good agreement with published experimental results. Our results are important to the development of electro‐optic and high‐speed electroabsorption quantum well devices.

Time‐resolved band‐to‐band photoluminescence offers a quick and contactless technique for determining the photoexcited free carrier lifetime in GaAs samples with deep traps.

We report the first measurements of perpendicular field electroabsorption (quantum confined Stark effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well suited for integrated optics. The absorption edge shifts to longer wavelengths with increasing field by as much as 40 meV, giving a modulation depth>10 dB. The strong dichroism present in this geometry is retained even at high fields, making polarization‐sensitive electro‐optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self‐electro‐optic effect with 20:1 on/off ratio.

The warpage of GaAs‐on‐Si wafers, caused by the different thermal expansion coefficients of GaAs and Si, has been studied as a function of the GaAs thickness on 3‐in.‐diam Si wafers. The warpage increases from 7 to 52 μm as the GaAs layer thickness increases from 1.2 to 4.2 μm. Under vacuum clamping conditions the GaAs/Si wafers can be forced to the original flatness. By growing GaAs selectively through a Si shadow mask as islands of 1 mm×1 mm size with a periodicity of 2 mm in a 5 cm×5 cm central area of the wafer, the warpage is reduced considerably. Spatially resolved cathodoluminescence (CL) spectra indicated that the tensile strain is reduced significantly within 10 μm from the edge of the growth. Near the edge, the CL intensity is also increased indicating a reduction in nonradiative recombination at defects. The use of the Si shadow mask to obtain patterned growth is relatively simple, requiring no processing step before or after the growth, and has a great potential in the integration of GaAs and ...

We demonstrate a combination of focused Ga beam writing and dry etching techniques to pattern InP wafers in a common vacuum chamber. Surface steps on the order of 1000 A can be efficiently prepared using moderate Ga ion fluences. The implanted areas exhibit a faster etch rate, even for Ga doses below ∼1014 cm−2. The implantation damage is removed by the low‐energy Cl‐assisted ion beam etching as shown by the high quality of p‐n junctions grown on etched surfaces. GaInAs/InP heterostructures grown on in situ patterned substrates show excellent morphology and high luminescence efficiency.

The first investigation of nonlinear absorption in InGaAs/InAlAs multiple quantum wells using picosecond and cw infrared lasers is presented. The nonlinearity is demonstrated to be due to plasma‐induced excitonic bleaching. The measured saturation densities agree with those predicted by theory.

We propose a new two‐coupled‐waveguide structure for second harmonic generation. An input TEω0 mode is phase matched to a harmonic TM2ω1 mode by varying the separation between the guides. Calculation of conversion efficiency in an AlGaAs structure gives 12% for 10 mW of input power at 1.3 μ over a 2‐mm phase‐matched length.

The first observation of strong and well‐resolved exciton peaks in the room‐temperature absorption spectra of infrared band‐gap multiple quantum well structures (MQW’s) is reported. Assignment of the optical resonances in the absorption spectra of GaInAs/AlInAs MQW’s yields the material parameters of this new heterojunction. The discontinuities of the conduction and valence bands are found to be ΔEc=0.44 eV and ΔEv=0.29 eV, respectively.